Lamps send out light in all directions. Without a shade or reflector, this light is only blocked by the base of the lamp. In order to make better use of this light, the lamps are used with reflectors and lenses. The reflectors reflect light emanating from one side of the lamp to another direction, and lenses refract the light so that it traveling in a different and preferred direction when it passes from a lens than when it entered the lens.
Light is a form of energy and should therefore be conserved and not wasted. Light can also become a form of pollution if it is directed where it is interferes with other activities, such as when light intended to illuminate the ground is partially directed into the sky only to obscure the stars. Control of a light beam is therefore important for three reasons, (1) light should be directed where it is needed so that it does what it is intended to do: illuminate an area for example; (2) it should not be wasted by directing it where it serves no purpose; and (3) it should not be directed where it interferes with other activities.
Controlling light from lamps is not as simple as it might sound. Especially when using lamps to illuminate large areas of ground outside at night. The goal of outdoor illumination, generally speaking, is to spread light from a simple lamp over as wide an area as possible and as evenly as possible but not to allow any light to be directed upwardly.
For example, see the lighting optical system of Jones as described in U.S. Pat. No. 4,591,960 which is intended to uniformly illuminate a large area using multiple reflectors. FIG. 3 of Jones shows a candle power distribution curve achieved by his system. This type of curve is commonly used to compare the efficiencies of lighting systems.
Often light is directed upwardly at an object in such a way that little of the light actually reaches the object and much is directed into the sky where it serves no purpose or blocks the view of the stars. An example of this is illumination of flags. Meyer in U.S. Pat. No. 3,752,975 teaches a light at the top of a flag pole for illuminating the flag from above rather than below but his light does not provide the lateral range for illuminating an unfurled flag.
Parabolic reflectors are well known in illuminating systems, especially those where the light is to be directed downwardly. Parabolic reflectors by definition tend to keep light rays parallel when the lamp located at the focus of the parabola so that a parabolic reflector does not disperse light but does illuminate a small area. If the parabola is directed downwards and its edge is extended below the focus of the parabola and the lamp, it will cutoff any upward light. See for example, the device described by Thompson in U.S. Pat. No. 5,329,438.
Many lights use visors or reflectors that are less vertical than that shown in Thompson's device to allow some spread of the light in a horizontal direction.
Nonetheless, there remains a need for a reflector that better achieves the goal of an even, downward-only, widespread light pattern, especially for use outdoors and in high bays.